As an information device that optically records and/or reproduces information, an optical memory system in which an optical disk such as a CD (compact disc), a DVD, or a BD (Blu-Ray disc), an optical card, or the like is used as an information recording medium is put to practical use.
In order to realize a further increase in a recorded information amount, there have been proposed an information device that performs high-density optical recording using near-field light capable of realizing a very small spot equal to or smaller than a diffraction limit of light and an information recording medium used in the information device. For example, an information recording medium disclosed in Patent Document 1 is proposed. A conventional information device in which such an information recording medium is used is explained below.
FIG. 33 is a perspective view showing a near-field light generation element and the information recording medium of the conventional information device. In a conventional information recording medium 103 shown in FIG. 33, a plurality of recording regions 104 having a size (about 3 to 30 nm) sufficiently smaller than the wavelength of recording light 105 are regularly arrayed two-dimensionally on a substrate 101. The recording regions 104 are configured from a phase change recording material such as GeTe—Sb2Te3. Note that array periods of the recording regions 104 in the X direction and the Y direction in the figure are respectively indicated by Λx and Λy, the height of the recording regions 104 is indicated by h, the size (the width) of the recording regions 104 in the Y direction is indicated by w, and an interval between the recording regions 104 is indicated by s. Λx, Λy, w, and s are sizes equal to or smaller than the diffraction limit of light and sufficiently smaller than a recording wavelength, and Λy=w+s.
In a near-field light generating element 109, a triangular metal film is arranged in parallel to an arrangement surface (the XY plane) of the recording regions 104 such that the longitudinal direction thereof is set as the Y direction and is arranged close to the recording regions 104 such that a working distance WD is about several tens nm from the arrangement surface.
Recording light 105 of linearly polarized light in the Y direction (a polarization direction 108), in which plasmon resonance tends to occur, is irradiated on the near-field light generating element 109. As a result, surface plasmon resonance is induced in the metal film of the near-field light generating element 109. Near-field light (near-field light having a polarization direction parallel to the polarization direction 108) with electric field intensity greatly increased compared with incident light is generated from a distal end portion (near the vertex of the triangular shape) of the near-field light generating element 109 (the near-field light is not shown in the figure).
The generated near-field light is irradiated on the recording region 104 arranged near the distal end portion, whereby the recording region 104 changes in a phase (from crystal to amorphous or from amorphous to crystal). Information can be recorded with one recording region set as a minimum unit.
However, the conventional information device explained above has a problem in that, when the recording regions 104 of the information recording medium 103 are further increased in density, information cannot be satisfactorily recorded.
Patent Document 1: WO 2010/116707